NOAA Technical Memorandum NMFS-AFSC-253 Calculation of the Geographic Area Sizes Used to Create Population Indices for the Alaska Fisheries Science Center Longline Survey by K. Echave, C. Rodgveller, and S.K. Shotwell U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Marine Fisheries Service Alaska Fisheries Science Center May 2013 NOAA Technical Memorandum NMFS The National Marine Fisheries Service's Alaska Fisheries Science Center uses the NOAA Technical Memorandum series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible. Documents within this series reflect sound professional work and may be referenced in the formal scientific and technical literature. The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries Science Center continues the NMFS-F/NWC series established in 1970 by the Northwest Fisheries Center. The NMFS-NWFSC series is currently used by the Northwest Fisheries Science Center. This document should be cited as follows: Echave, K., C. Rodgveller, and S.K. Shotwell. 2013. Calculation of the geographic area sizes used to create population indices for the Alaska Fisheries Science Center longline survey. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-253, 93 p. Reference in this document to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. NOAA Technical Memorandum NMFS-AFSC-253 Calculation of the Geographic Area Sizes Used to Create Population Indices for the Alaska Fisheries Science Center Longline Survey by K. Echave, C. Rodgveller, and S.K. Shotwell Alaska Fisheries Science Center Auke Bay Laboratories 17109 Lena Point Loop Road Juneau, AK 99801 www.afsc.noaa.gov U.S. DEPARTMENT OF COMMERCE Rebecca M. Blank, Acting Secretary National Oceanic and Atmospheric Administration Kathryn D. Sullivan, Acting Under Secretary and Administrator National Marine Fisheries Service Samuel D. Rauch III, Acting Assistant Administrator for Fisheries May 2013 This document is available to the public through: National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, VA 22161 www.ntis.gov ABSTRACT Geographic area sizes (km2) are used for computing abundance indices for sablefish and other groundfish species caught in the Alaska Fisheries Science Center’s annual longline survey. These areas were devised before geographic information systems (GIS) and accurate bathymetric maps were available. In addition, there was poor documentation for how the currently used area measurements were determined. With new technology, area sizes can be defined using GIS to ground truth the area sizes currently being used for computing abundance indices. Additionally, because the survey was originally intended for sablefish, and their habitat is primarily in depths from 200 to1,000 m, area sizes were not determined for areas shallower than 200 m. A substantial amount of survey effort is placed in the 151-200 m depth range and several species of interest are commonly caught in these depths. Using ArcView GIS 9.3 and GEBCO_08 bathymetry source, geographic area sizes were recalculated and compared with existing values. In addition, area sizes for shallow stratum, consisting of depths between 151 and 200 m, were created, and documentation is provided for how the currently used area measurements were determined. Recalculated area sizes and geographic area sizes utilized in the AFSC longline and RACE trawl surveys were generally similar across the WGOA and CGOA, with larger differences occurring in the EGOA and in the gullies where boundary lines were hard to decipher. Where differences occurred, recalculated values were generally smaller. iii CONTENTS ABSTRACT ................................................................................................................................... iii LIST OF TABLES ......................................................................................................................... vi LIST OF FIGURES ...................................................................................................................... vii ACRONYMS............................................................................................................................... viii INTRODUCTION .......................................................................................................................... 1 HISTORICAL ACCOUNTING OF THE CURRENT GEOGRAPHIC AREA SIZES ................ 2 Sasaki’s Methods......................................................................................................................... 2 Brown and Rose, GOA RACE Trawl Survey Methods .............................................................. 3 Haight Methods ........................................................................................................................... 4 Sigler Methods for the AFSC Longline Survey .......................................................................... 5 METHODS FOR NEW GEOGRAPHIC AREA SIZE CALCULATIONS FOR THE LONGLINE SURVEY ................................................................................................................... 6 RESULTS AND DISCUSSION ..................................................................................................... 7 Area Delineation ............................................................................................................................. 9 Southeast Outside Geographic Area ............................................................................................... 9 Dixon Entrance...................................................................................................................... 10 Iphigenia Gully...................................................................................................................... 10 Ommaney Trench. .................................................................................................................. 10 Spencer Gully Southeast........................................................................................................ 11 West Yakutat Geographic Area .................................................................................................... 11 Spencer Gully Yakutat ........................................................................................................... 11 Alsek Strath............................................................................................................................ 11 Yakutat Valley........................................................................................................................ 12 W-Grounds............................................................................................................................. 12 Kodiak Geographic Area .............................................................................................................. 12 Amatuli Gully......................................................................................................................... 12 Chirikof Geographic Area ............................................................................................................. 13 v Shelikof Trough...................................................................................................................... 13 Shumagin Gully ..................................................................................................................... 13 Shumagin Geographic Area .......................................................................................................... 13 Aleutian Islands Area .................................................................................................................... 14 Eastern Bering Sea Area ............................................................................................................... 14 CITATIONS ................................................................................................................................. 15 TABLES ....................................................................................................................................... 16 FIGURES ...................................................................................................................................... 26 Appendix 1. Haight’s 1987 In-House Technical Report .............................................................. 49 Appendix 2. Sigler’s Unpublished Methods from 1989 ............................................................... 8(cid:22) Appendix 3. Haight’s 1986 Unpublished Table ........................................................................... 8(cid:28) Appendix 4. Brown and Rose’s 1985 Unpublished Table ............................................................ (cid:28)(cid:20) vi LIST OF TABLES Table 1a. Calculated area sizes by depth stratum and source for the Gulf of Alaska. .................. 16 Table 1b. Calculated geographic area sizes by depth stratum and source within the West (W), Northwest (NW), Southwest (SW), East (E), Northeast (NE), and Southeast (SE) Aleutian Islands. .......................................................................................................................................... 17 Table 1c. Calculated geographic area sizes by depth stratum and source within Regions I, II, III, and IV of the Eastern Bering Sea . ................................................................................................ 18 Table 1d. Calculated area sizes by depth stratum and source for defined gullies within the Gulf of Alaska. .......................................................................................................................................... 19 Table 1e. Calculated geographic area sizes by depth stratum and source within East (E) and West (W) Yakutat. ................................................................................................................................. 20 Table 2. The total number of stations per geographic area, the number of stations with consistent effort in depths < 200 m (85% of years had sampling in the < 200 m depths), and the average percentage of effort in each depth stratum (e.g., 100-200 m) from 1996 to 2011 on the AFSC longline survey .............................................................................................................................. 21 Table 3. Boundaries delineating outside vs. inside areas defined by Sigler in 1989. ................... 22 Table 4. Calculated area sizes by depth stratum and source. ........................................................ 22 Table 5. The average number and length of hachis set in each geographic area within the 151­ 200 m stratum from 1996 to 2011. The approximate widest distance of the shelf within the 151­ 200 m is also included................................................................................................................... 23 Table 6. A comparison of the current area sizes designated as slope habitat used by the RACE trawl survey (von Szalay et al. 2010, appendix table A-1) to the new area sizes calculated by this study…………………………………………..………………………………….………………24 Table 7. A comparison of all the current area sizes used by the RACE trawl survey (von Szalay et al. 2010, appendix table A-1) to the new area sizes calculated by this study. These areas include habitat designated as gullies, shelf, and slope …………………………………………..25 vii LIST OF FIGURES Figure 1. Map of the Alaska Fisheries Science Center’s annual longline survey stations and sablefish management areas. ........................................................................................ 26 Figure 2. Defined “inside” and “outside” waters as defined by Sigler in 1989. ........................... 27 Figure 3. A drawing depicting three sampling scenarios in one geographic area and their various methods of shallow stratum calculation.. ..................................................................... 28 Figure 4. Southeast Outside Geographic Area. ............................................................................. 29 Figure 5. Dixon Entrance. ............................................................................................................. 30 Figure 6. Iphigenia Gully. ............................................................................................................. 30 Figure 7. Ommaney Trench. ......................................................................................................... 31 Figure 8. Spencer Gully Southeast (SE). ...................................................................................... 32 Figure 9. West Yakutat Geographic Area. .................................................................................... 34 Figure 10. Spencer Gully Yakutat (YAK). ................................................................................... 35 Figure 11. Alsek Strath. ................................................................................................................ 36 Figure 12. Yakutat Valley. ............................................................................................................ 37 Figure 13. W-Grounds. ................................................................................................................. 38 Figure 14. Kodiak Geographic Area. ........................................................................................... 39 Figure 15. Amatuli Gully. ............................................................................................................. 40 Figure 16. Chirikof Geographic Area. .......................................................................................... 40 Figure 17. Shelikof Trough. .......................................................................................................... 41 Figure 18. Shumagin Gully. .......................................................................................................... 42 Figure 19. Shumagin Geographic Area. ....................................................................................... 44 Figure 20. East Aleutian Islands Geographic Area ....................................................................... 45 Figure 21. West Aleutian Islands Geographic Area ..................................................................... 46 Figure 22. Eastern Bering Sea Regions I and II............................................................................ 47 Figure 23. Eastern Bering Sea Regions III and IV. ...................................................................... 48 viii